Field of the Invention
The present invention relates to an ink set and an ink jet recording method using the ink set.
Description of the Related Art
In recent years, inks containing pigments as coloring materials (pigment inks) have been widely used in order to record images having higher toughness including gas resistance and light resistance, as the inks used for an ink jet recording method. The pigments are particulate, and thus images recorded with the pigment inks on a recording medium having a glossy surface (what is called glossy papers) unfortunately have insufficient gloss clarity as compared with images recorded with dye inks in which dyes are dissolved in an aqueous medium. The “gloss clarity” is one of the characteristics indicating the sharpness of an image recorded on the surface of a recording medium. For example, an image having low gloss clarity has a blurred appearance, whereas an image having high gloss clarity has a clear appearance. The gloss clarity can be evaluated by a haze value, for example. Specifically, a lower haze value indicates higher gloss clarity.
In addition, images recorded with the pigment ink cause what is called a bronzing phenomenon that light having a different color from that of incident light is reflected. For example, images recorded with a cyan ink containing phthalocyanine may cause a reddish bronzing phenomenon, and images recorded with an ink containing carbon black may cause a yellowish bronzing phenomenon.
To solve these problems, various techniques have been studied. For example, in order to improve the glossiness and to suppress the bronzing phenomenon of images recorded with a pigment ink, an ink set including a clear ink containing a water-soluble resin has been disclosed (Japanese Patent Application Laid-Open No. 2009-197211). Separately, an ink set including a clear ink containing a urethane resin has been disclosed (Japanese Patent Application Laid-Open No. 2013-064082 and Japanese Patent Application Laid-Open No. 2010-520324). The ink set improves the anti-scratching properties or the glossiness of images recorded with a pigment ink.
The inventors of the present invention have used the conventional clear inks described in Patent Documents to study the gloss clarity and the bronzing resistance of images recorded with a pigment ink. The result has revealed that the effects of improving the gloss clarity and the bronzing resistance of images are not achieved at high levels by using any of the clear inks. In addition, a new problem commonly caused when conventional clear inks are used has been found during the above study. Specifically, the newly found problem is that when a clear ink is applied onto the image recorded with a pigment ink, reflected light coloring that differs from the bronzing phenomenon is caused, or glossiness is changed, and “unevenness” is caused in some areas in the image. The “unevenness” is caused by the following mechanism. That is, light is reflected by both the surface of a “pigment layer” constituting an image and the surface of a “resin layer” formed on the “pigment layer” by a resin particle in a clear ink to generate two kinds of reflected light, and the two kinds of reflected light cause an “fringe phenomenon”. Hereinafter, the unevenness caused by the above “fringe phenomenon” is called “fringe unevenness”.
The problem of “fringe unevenness” caused by using conventional clear inks has not been recognized in Japanese Patent Application Laid-Open No. 2009-197211, 2013-064082 and Japanese Patent Application Laid-Open No. 2010-520324. In other words, the “fringe unevenness” has not been considered and is a new problem. When the ink sets disclosed in Japanese Patent Application Laid-Open No. 2009-197211 and Japanese Patent Application Laid-Open No. 2013-064082 are used, the suppressive effect of the bronzing phenomenon is slightly observed, but the improvement effect of the gloss clarity of images or the suppressive effect of the fringe unevenness cannot be achieved. When the ink set disclosed in Japanese Patent Application Laid-Open No. 2010-520324 is used, the improvement effect of the gloss clarity of images and the suppressive effect of the bronzing phenomenon are slightly observed, but the suppressive effect of the fringe unevenness cannot be achieved.
An object of the present invention is thus to provide an ink set enabling the recording of images that have excellent gloss clarity and bronzing resistance and have suppressed an occurrence of fringe unevenness when a clear ink and a pigment ink are used in combination. Another object of the present invention is to provide an ink jet recording method using the ink set.